<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            display: flex;
            justify-content: space-between;
            /*align-items: flex-end;!*交叉轴上单行元素从下到上排列 *!*/
            align-items: center;/*交叉轴上单行元素在中间 */
            /*align-items: stretch;!*交叉轴上将元素拉伸，但是不能设置子项目的高度*!*/
            width: 90%;
            height: 600px;
            background-color: skyblue;
        }
        span{
            width: 100px;
            height: 100px;
            background-color: greenyellow;
        }
    </style>
</head>
<body>
<!--flex-direction-->
<div class="">
    <span>1</span>
    <span>2</span>
    <span>3</span>
    <span>4</span>
</div>
</body>
</html>